Doping Silver Increases the Au38(SR)24 Cluster Surface Flexibility

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• 作者：Bei Zhang ; Thomas Bürgi
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：March 3, 2016
• 年：2016
• 卷：120
• 期：8
• 页码：4660-4666
• 全文大小：429K
• ISSN：1932-7455

文摘

Multiple Ag atoms were doped inside Au₃₈(SCH₂CH₂Ph)₂₄ nanoclusters using the metal exchange method for the first time for the synthesis of Ag_xAu_38–x(SCH₂CH₂Ph)₂₄. MALDI-TOF mass spectrometry revealed the time dependence of the synthesis. Cluster species with different numbers of Ag atoms (different x values) migrate differently on a chromatography (HPLC) column, which allows one to isolate cluster samples with a narrowed distribution of exchanged metal atoms. The enantiomers of selected Ag_xAu_38–x(SCH₂CH₂Ph)₂₄ samples (average x = 6.5 and 7.9) have been separated by HPLC. Doping changes the electronic structure, as is evidenced by the significantly different CD spectra. UV–vis spectra of the doped sample also show diminished features. The temperature required for complete racemization follows Au₃₈ > Ag_xAu_38–x (x = 6.5) > Ag_xAu_38–x (x = 7.9). To our surprise, the racemization of Ag_xAu_38–x(SCH₂CH₂Ph)₂₄ (x = 7.9) occurred even at 20 °C. Racemization involves a rearrangement of the staple motifs at the cluster surface. The results therefore show an increased flexibility of the cluster with increasing silver content. The weaker Ag–S bonds compared to Au–S are proposed to be at the origin of this observation. The experimentally determined activation energy for the racemization is ca. 21.5 kcal/mol (x = 6.5) and 19.5 kcal/mol (x = 7.9), compared to 29.5 kcal/mol for Au₃₈(SCH₂CH₂Ph)₂₄, suggesting no complete metal–S bond breaking in the process.